1. Field of the Invention
The invention relates to a control device, and more particularly to a control device for compensating path mismatching in an automatic power control circuit.
2. Description of the Related Art
FIG. 8 shows a characteristic curve of a laser diode. When an input current provided to a laser diode is less than a threshold current Ith, the laser diode serves as a light-emitting diode (LED), thus, light emitted from the laser diode is less bright. When the input current exceeds the threshold current Ith, the light emitted from the laser diode increases rapidly when the input current increases.
When temperature increases, the threshold current Ith increases. Thus, an automatic power control (APC) circuit is added for controlling the input current. The APC circuit, however, suffers from mismatching due to manufacturing procedures.